1. Field of the Invention
The present invention relates to lithium secondary batteries employing spinel-structured lithium-manganese complex oxide as the cathode active material thereof.
2. Description of the Related Art
In the recent years, there has been accelerated development of down-sized and cordless design schemes in the field of electronics apparatus or equipment. In view of this trend, secondary batteries are of increasing interest since these have increased applicability as the power supply for such electronic equipment due to their capability of size reduction and high electrical energy density. The 4-V class lithium secondary batteries of the non-aqueous electrolytic solution type have been commercialized as secondary batteries satisfying the needs of the new equipment.
A lithium secondary battery generally includes (a) an cathode having a lithium-containing compound as the active material, (b) an anode having a material capable of absorbing and desorbing lithium, such as a carbon material, or lithium metal as the active material and (c) a separator containing a non-aqueous electrolytic solution or a solid electrolyte. The lithium-containing compound used as the active material of the cathode may include, for example, LiCoO.sub.2, LiNiO.sub.2 and LiMn.sub.2 O.sub.4. Recently, attention has been drawn to the spinel-structured lithium-manganese complex oxides, such as LiMn.sub.2 O.sub.4, as the natural resource for the complex oxide because it is expected to exist in a large enough quantity to be inexpensive and provide a stable supply. Accordingly, various lithium secondary batteries comprising the complex oxide as an active material of the cathode has been proposed.
For example, Japanese Laid-Open Patent Application No. 6-333562 discloses a lithium secondary battery comprising an LiMn.sub.2 O.sub.4 type compound as the cathode active material, in which the compound is in the form of spherical particles having uniformly roughened surfaces and having a median diameter of from 0.5 to 0.6 .mu.m while being distributed within a particle size range of 0.1 to 1.1 .mu.m. Japanese Laid-Open Patent Application No. 8-69790 discloses a lithium secondary battery comprising a lithium-manganese complex oxide as the cathode active material, in which the complex oxide has specific surface area of from 0.05 to 5.0 m.sup.2 /g.
However, the conventional lithium secondary batteries comprising such a spinel-structured lithium-manganese complex oxide as the active material are not still satisfactory with respect to the battery capacity and the charge-discharge cycle characteristics.
It is therefore an object of the present invention to provide a lithium secondary battery of large battery capacity with enhanced charge-discharge cycle characteristics.